290 Account of a Filaria in a Horse’s Eye. 
feeding in a particular manner. But if such transitions occur in 
worms, we should sometimes observe them while undergoing the 
process, for it would be contrary to all analogy to suppose that the 
change would be sudden. But we see no such transitions; we 
never find these animals “half way between what they were and 
what they are.” No zoologist, not even Bremser, who devoted 
twelve years of his life to the study of Entozoa, ever witnessed 
any such change; indeed, he states expressly, “that after having 
diligently examined 15,000 specimens of worms in the Cabinet 
of Vienna, he never was for one moment at.a loss to say which 
were intestinal worms and which were not.” If worms then ori- 
ginate within the body, how do they originate ?—what are the 
obstacles in the way of our adopting the theory of spontaneous 
generation? In the first place, if they can be formed by the 
mere combination of inorganic elements, we may well ask, why 
they should be furnished with reproductive organs? No such 
- ereations or combinations have ever been observed, and therefore 
the fact of their occurrence is a matter of mere supposition. The 
only argument on which this hypothesis may be said to rest, is 
our ignorance of the precise mode of their origin, and derives no 
support from analogy. 
If this theory be true, it is difficult to explain why the law 
should be confined to the lower classes of animals, and not also 
extend to the higher. By some fortuitous concourse of atoms, 
we should expect, occasionally, to see a man, a quadruped, or a 
bird, spring up from some dunghill, or fermenting vat ; but this 
is a phenomenon which even Ovid never dreamed of. 
The production of certain species of vegetables was once aS 
difficult to explain, as it now is to account for the origin of intes- 
tinal worms; but late investigations have removed these diffieul- 
ties, and shown that they are propagated in the usual manner by 
seed or reproductive granules. Thus it is observed that white 
clover is ready to spring up on soils which have been rendered 
alkaline by the strewing of wood-ashes, or the burning of weeds; 
ground newly turned up by the plough is found to produce plants 
dissimilar to any in their neighborhood ; parasitic fung? sprout up 
“upon decaying organized substances, and even in the interior 
cheese; &c, Dr. Good remarks that he “has seen a hop-ground 
jletely overrun and desolated by the Aphis humuli, or hop 
green-louse, within twelve hours after a honey-dew (which 1s 4 
